1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an apparatus for cutting a substrate and a method using the same. Although the present invention is suitable for a wide scope of application, it is particularly suitable for improving yield in manufacturing liquid crystal display devices.
2. Discussion of the Related Art
With the recent rapid development of information communication fields, the industries associated with displays adapted to display desired information are gaining importance. Of such information displays, cathode ray tubes (CRTs) have continuously drawn attention by virtue of advantages such as reproducibility of diverse colors and superior screen brightness. Due to the recent demand for large-size, portable and high-resolution displays, however, the development of flat panel displays is in high demand, in order to replace CRTs which are heavy and bulky.
Flat panel displays are applicable to wide and diverse fields such as computer monitors and monitors for both aircraft and spacecraft. As currently-developed or commercially-available flat panel displays, there are LCDs, electro-luminescent displays (ELDs), field emission displays (FEDs), plasma display panels (PDPs), and the like.
A process of manufacturing such flat panel displays usually involves separating a fragile mother substrate into a plurality of unit LCDs using a cutting process. On the mother substrate, a plurality of unit elements, such as semiconductor chips are formed in a matrix form to create large-scale integrated circuits.
There are basically two cutting process used for separating the fragile mother substrate, which may be made of glass, silicon, or ceramic. The first process is a dicing method in which cutting grooves are formed on the substrate using a diamond blade having a thickness of 50 to 200 μm while the diamond is rotated at high speed. The second process is a scribing method in which cutting grooves are formed on a surface of the substrate by a scribing wheel made of a diamond having a thickness of 0.6 to 2 mm, so as to form a crack in a thickness direction of the substrate.
The dicing method is suitable for cutting of a substrate formed with a thin film or a convex portion at a surface of the substrate because a very thin blade is used, as compared to the scribing method. In the dicing method, however, frictional heat is generated at a region where the blade performs a cutting process. Furthermore, since the cutting process is carried out under the condition in which cooling water is supplied to the cutting region, the dicing method is not considered to be a method suitable for a flat panel display which includes metal portions, such as Metal electrode layers or metal terminals.
In other words, in the dicing method, it is difficult to completely remove the cooling water after the cutting process. When moisture remains due to the incomplete removal of the cooling water, there may be a possibility that the metal portions of the flat panel display may be eroded. Furthermore, the dicing method has a problem of a prolonged cutting time, thereby lowering yield, as compared to the scribing method.
On the other hand, it is unnecessary to use cooling water in the scribing method. Accordingly, the scribing method exhibits superior throughput, as compared to the dicing method. Also, since the cutting time required in the scribing method is shorter than that of the dicing method, the scribing method has an advantage in better yield.
FIG. 1 is a cross-sectional view illustrating the related art LCD device. This LCD device is manufactured in accordance with the following method. For simplicity, descriptions will be made only in conjunction with one pixel region.
As shown in FIG. 1, a gate electrode 11 of a conductive material, such as metal, is deposited on a first transparent substrate 10 at a predetermined region. A gate insulating film 12 of a silicon nitride (SiNx) or silicon oxide (SiO2) is then deposited over the entire upper surface of the first substrate 10 including the gate electrode 11.
Thereafter, an active layer 13 of amorphous silicon is formed on the gate insulating film 12 at a region corresponding to the gate electrode 11. An ohmic contact layer 14 is formed on the active layer 13 at regions corresponding to respective lateral edge portions of the active layer 13. The ohmic contact layer 14 is formed of doped amorphous silicon.
Source and drain electrodes 15 and 16, which are formed of a conductive material such as metal, are subsequently formed on the ohmic contact layer 14. The source and drain electrodes 15 and 16 constitute a thin film transistor T, together with the gate electrode 11. Meanwhile, although not shown in the drawing, the gate electrode 11 is connected to a gate line, and the source electrode 15 is connected to a data line. The gate line and the data line cross each other, and define a pixel region.
A protective film 17 is then formed over the entire upper surface of the first substrate 10 including the source and drain electrodes 15 and 16. The protective film 17 is formed of a silicon nitride, silicon oxide, or organic insulating material. The protective 17 has a contact hole 18 through which a predetermined portion of the surface of the drain electrode 16 is exposed. Thereafter, a pixel electrode 19 of a transparent conductive material is formed on the protective film 17 at the pixel region. The pixel electrode 19 is connected to the drain electrode 16 via the contact hole 18.
A first orientation film 20 is then formed over the entire upper surface of the first substrate 10 including the pixel electrode 19. The first orientation film 20 is polyimide, and has a surface on which the molecules of the first orientation film 20 are oriented in a predetermined direction. Meanwhile, a second transparent substrate 31 is arranged over the first substrate 10 while being vertically spaced apart from the first substrate 10 by a predetermined distance.
A black matrix 32 is formed on a lower surface of the second substrate 31 at a region corresponding to the thin film transistor T of the first substrate 10. Although not shown in the drawing, the black matrix 32 also covers a region except for the pixel electrode 19.
A color filter 33 is then formed on the second substrate 31 beneath the black matrix 32. Practically, color filters are arranged in the form of repeated filter patterns of red (R), green (G), and blue (B), each of which corresponds to one pixel region.
A common electrode 34 of a transparent conductive material is subsequently formed on the second substrate 31 beneath the color filter 33. A second orientation film 35 is then formed on the second substrate 31 beneath the common electrode 34. The second orientation film 35 is of polyimide, and has a surface on which the molecules of the second orientation film 35 are oriented in a predetermined direction. Then, a liquid crystal layer 40 is formed between the first orientation film 20 and the second orientation film 35.
The above-described LCD device is manufactured using an array substrate fabrication process involving formation of thin film transistors and pixel electrodes on a substrate to fabricate an array substrate, a color filter substrate fabrication process involving formation of color filters and a common electrode on another substrate to fabricate a color filter substrate, and a liquid crystal panel fabrication process involving arrangement of the fabricated substrates, injection and sealing of a liquid crystal material, and attaching polarizing plates, to thereby complete in fabricating a liquid crystal panel.
FIG. 2 is a flow chart illustrating the related art LCD manufacturing method.
In accordance with this method, a thin film transistor (TFT) array substrate including TFTs, and a color filter substrate including color filters are first prepared (S1), as shown in FIG. 2. The TFT array substrate is fabricated by repeatedly performing processes of depositing a thin film and pattering the deposited thin films. In this case, the number of masks used for patterning of thin films in the fabrication of the TFT array substrate represents the number of processes used in the fabrication of the TFT array substrate. Currently, research is being actively made to reduce the number of masks, thereby reducing the manufacturing cost.
The color filter substrate is fabricated by sequentially forming a black matrix for preventing light leakage through a region except for pixel regions, such as R, G, and B color filters and a common electrode. The color filters may be formed using one of a dyeing method, a printing method, a pigment dispersion method, an electro-deposition method, or the like. Currently, the pigment dispersion method is mostly used.
Thereafter, an orientation film is formed over each substrate to determine an initial alignment direction of liquid crystal molecules (S2). The formation of the orientation film is achieved using a process for coating a polymer thin film, and treating the surface of the polymer thin film such that the molecules of the polymer thin film on the treated surface are oriented in a predetermined direction. Generally, polyimide-based organic materials are mainly used for the orientation film. For the orientation method, a rubbing method is mostly used.
In accordance with the rubbing method, the orientation film is rubbed in a predetermined direction, using a rubbing cloth. This rubbing method is suitable for mass production because treatment for orientation can be easily achieved. Also, the rubbing method has advantages of stable orientation and easy control of a pre-tilt angle. Recently, an optical orientation method has been developed and practically used that achieves orientation using polarized beams.
Next, a seal pattern is formed at one of the two substrates (S3). The seal pattern is arranged around a region where an image is displayed. The seal pattern has a port for injecting a liquid crystal material, and serves to prevent the injected liquid crystal material from leaking.
The seal pattern is formed by forming a thermosetting resin layer to have a predetermined pattern. For the formation of the seal pattern, a screen printing method using a screen mask, and a seal dispenser method using a dispenser may be used.
Currently, the screen printing method is mainly used because it has a more convenient process. However, the screen printing method also has a drawback in that products with poor quality may be produced because the screen mask may come into contact with the orientation film. Furthermore, the screen mask cannot easily cope with a large-sized substrate size. For this reason, substitution of the seal dispenser method for the screen printing method is being gradually increased.
Subsequently, spacers having a predetermined size are sprayed on one of the TFT array substrate and the color filter substrate to maintain an accurate and uniform space between the two substrates (S4). For a method of spraying spacers, there are a wet spray method in which spacers are sprayed in a state of being mixed with alcohol, and a dry spray method in which just spacers are sprayed alone. For the dry spray method, there is an electrostatic spray method using static electricity and an ionic spray method using pressurized gas. Since LCDs are vulnerable to static electricity, the ionic spray method is mainly used.
Thereafter, the two substrates of the LCD (i.e., the TFT array substrate and the color filter substrate) are arranged such that the seal pattern is interposed between the substrates. In this state, the seal pattern is cured under pressure to attach the substrates (S5). In this case, the orientation films of the substrates face each other, and the pixel electrodes and the color filters correspond to each other one by one.
Next, the joined substrates are cut to be separated into a plurality of unit liquid crystal panels (S6). Generally, a plurality of liquid crystal panels, each of which will be one LCD device, are formed on one substrate sheet, and are then separated into individual ones, to achieve an enhancement in manufacturing efficiency and a reduction in manufacturing costs.
The liquid crystal panel cutting process includes a scribing process for forming a crack in the surface of each substrate using a scribing wheel made of a diamond material having hardness higher than that of the substrate, which is made of, for example, glass. The liquid crystal panel cutting process further includes a breaking process for positioning a breaking bar at a portion of the substrate where the crack is formed. Subsequently, a predetermined pressure is applied to the breaking bar, thereby cutting the substrate in a direction along which the crack extends.
Next, a liquid crystal material is injected between the two substrates of each liquid crystal panel (S7). For the injection of the liquid crystal, a vacuum injection method is mainly used which utilizes a pressure difference between the interior and exterior of the liquid crystal panel. Micro air bubbles may be present amongst the liquid crystal molecules injected into the interior of the liquid crystal panel, so that bubbles may be present in the interior of the liquid crystal panel, thereby causing the liquid crystal panel to have poor quality. In order to prevent such a problem, accordingly, it is necessary to perform a de-bubbling process in which the liquid crystal is maintained in a vacuum state for a prolonged time to remove bubbles.
After completion of the liquid crystal injection, the injection port is sealed to prevent the liquid crystal from leaking out of the injection port. The sealing of the injection port is achieved by coating an ultraviolet-setting resin over the injection port, and irradiating ultraviolet rays to the coated resin, thereby setting the coated resin.
Next, polarizing plates are attached to the outer surfaces of the liquid crystal panel fabricated in the above-mentioned manner, and driving circuits are then connected to the liquid crystal panel. Thus, the fabrication of an LCD device is complete (S8). Hereinafter, a related art substrate cutting apparatus and a related art substrate cutting method using the same will be described with reference to the annexed drawings.
FIG. 3 is a schematic view illustrating a related art scribing device. As shown in FIG. 3, the related art scribing device includes a table 51, on which a substrate G is positioned, a vacuum chucking unit (not shown) adapted to fix the substrate G to the table 51, and a pair of parallel guide rails 52 for pivotally supporting the table 51 in a suspended state while allowing the table 51 to be movable in a Y-axis direction. The scribing device also includes a ball screw 53 for moving the table 51 along the guide rails 52, a guide bar 54 installed above the table 51 such that the guide bar 54 extends in an X-axis direction, and a scribing head 55 mounted on the guide bar 54 such that the scribing head 55 can slide in the X-axis direction along the guide bar 54. The scribing device further includes a motor 56 for sliding the scribing head 55, a tip holder 57 mounted to a lower end of the scribing head 55 such that the tip holder 57 is vertically movable while being rotatable, and a scribing wheel 1 rotatably mounted to a lower end of the tip holder 57.
In the related art substrate cutting method using the above-mentioned scribing device, a crack having a certain depth is formed in a substrate to be cut, in accordance with rotation of the scribing wheel 1. The crack-formed substrate is then fed to a breaking device, in which a pressure is applied to the substrate along the crack by a breaking bar, thereby cutting the substrate.
FIGS. 4 and 5 are schematic views respectively illustrating scribing and breaking processes involved in the related art substrate cutting method. In the scribing process, the scribing wheel or cutting wheel 82 brings into contact with the surface of a substrate 81, as shown in FIG. 4. In such a state, the scribing wheel 82 is rotated along the substrate 81 while applying pressure of about 2.40 Kgf/cm2 to the substrate 81. As a result, a crack 83 with a certain depth is formed in the surface of the substrate 81 along a track of the scribing wheel 82.
Thereafter, the breaking process is carried out along the crack 83 in the surface of the substrate 81 to cut the substrate 81. That is, as shown in FIG. 5, a breaking bar 84 is arranged on the substrate 81 in which the crack 83 has been formed in the scribing process. The portion of the breaking bar 84 coming into direct contact with the surface of the substrate 81, that is, a portion A of the breaking bar 84, is made of a material which is sufficiently hard, but does not form scratches on the surface of substrate 81, such as urethane rubber.
Next, pressure is momentarily applied to the substrate 81 by the breaking bar 84 under the condition in which the breaking bar 84 is accurately aligned with the crack 83. As a result, the crack 83 is extended, thereby causing the substrate 81 to be cut.
Thereafter, a grinding process is carried out using a grindstone having a predetermined mesh size, in order to grind cut surfaces and corners of the substrate formed after the scribing and breaking processes.
Thus, in accordance with the related art substrate cutting method, a plurality of liquid crystal panels formed on the substrate are separated into a plurality of unit LCD devices in accordance with the above-mentioned scribing and breaking processes. However, the above-mentioned related art substrate cutting method has various problems. For example, the scribing wheel used in the scribing process for cutting the substrate is expensive and has a short lifespan, necessitating periodic replacement thereof. For this reason, an increase in manufacturing cost is incurred.